This invention relates to optical decoders and, more particularly, to the optical decoding of information from the screen of a television receiver, monitor, or other display.
Considerable attention is being given to the use of television assistance as an education and training tool. In such uses, it often is desirable to present various information to the user/viewer whereby he can make a choice. For example, in a testing situation it is often desirable to present a question to the user and have him select one of a plurality of possible answers. The same application is, of course, useful for entertainment as the television industry has made quizzes an important form of entertainment for the public.
In my U.S. Pat. No. 3,737,566 for a "Television Coder and Decoder", I describe apparatus for decoding information from the screen of a television receiver. The decoding consists of determining which one of a plurality of displayed coded spots on a television receiver screen is the correct answer to, for example, a question. A number of coded spots are presented on the television screen and the correct answer is coded differently from the incorrect answers. In the coding scheme of this patent, one of the spots, the correct answer, would be coded to flash an even number of times while all the rest would be coded to flash an odd number of times, or vice versa. The decoder detects this difference. While this system works very well, it does require that the user put his optical decoding device, photosensor, on the correct spot prior to its starting to flash so that the decoder will be able to determine whether it flashed an even or odd number of times. This can be problemsome since there are many instances where it is desirable to have the spot selected after the flashing has begun and not necessarily requiring the decoder to be put next to the spot prior to the flashing.
In my U.S. Pat. No. 3,993,861 for a "Digital Video Modulation and Demodulation System", I describe a system for providing digital data via a flashing spot which allows significantly more data to be presented over the odd/even data presented in the system of U.S. Pat. No. 3,737,566, however, also in this case it is necessary that the user place his lightpen on the flashing spot prior to its beginning to flash in order to obtain the entire message.
Both of these systems suffer from the limitation that the photosensor must be in place and facing the spots on the CRT before the encoded sequence of light spots start flashing. Doing otherwise would result in missing the beginning of a coded sequence. To preclude this problem, the coded sequence could be repeated and start and stop data be provided to enable the sensor unit to know when the beginning of a code sequence has occurred. Of course, this requires circuitry to recognize start and stop codes. This has been done in applications of the teachings of said U.S. Pat. No. 3,993,861, but it is not an optimum solution to the problem for certain applications, such as those requiring very inexpensive decoders.
Accordingly, it is an object of this invention to provide an improved optical decoder for displays.
It is another object of this invention to provide a decoder which will permit decoding of light spots displayed on the face of a display notwithstanding that the photosensor is placed on the display screen after spot transmission is in progress.
It is a further object of this invention to provide an improved simple decoder which can distinguish between two or more differing codes which will not be distinguishable by the naked eye.